The newest Anthropocene epoch is characterized by two interrelated human activity-associated phenomena—exhaustion of natural resources along with strong environmental footprint from one side and vigorous development of cutting-edge technologies such as nanotechnology, artificial photosynthesis and synthetic biology from the other side. To address global energy challenges it is necessary to develop efficient yet environmentally-friendly energy sources as an alternative to hydrocarbons feedstocks. Biologically-inspired photocatalytic transformation of solar energy and water to clean fuels such as hydrogen using semiconductors is among the most promising dynamically evolving renewable energy technologies. “Greener” schemes of photocatalytic visible-light hydrogen production along with inorganic material utilize biological structures capable of water splitting, light-harvesting or proton reduction. Applicants have been developing visible light-driven nanobio photocatalysts for hydrogen production based on non-covalent assemblies of the natural membrane proton pump bacteriorhodopsin bR and TiO2 semiconductor nanoparticles. While in a natural environment the neat protein machinery of the bR proton pump carries sunlight-driven transmembrane proton transfer providing an electrochemical gradient for synthesis of ATP, in engineered water splitting systems in addition to preserved inherent function it also acts as a visible light photosynthesizer that injects photoexcited electrons into the conduction band of a semiconductor.
With the advent of modern life science technologies, or “synthetic life”, it became achievable to design and produce key functional components of life, including chemically synthesized DNA circuits, proteins and artificial cell membranes from scratch. For example, a living bacteria can be re-programmed via transplantation of chemically-synthesized genome for rebooting cell with new desired function such as biosyntheses of fine chemicals, protein therapeutics or renewable biofuels. On the other hand, it also became achievable to accomplish one of the core cellular function, protein biosynthesis, outside of a living cell confined space, or “cell-free,” through assembly of key logic elements of a cell, namely artificial biomembrane as a template, synthetic DNA as a blueprint, an isolated biological translation machinery of ribosome along with supply of energy-rich chemicals, aminoacids, cofactors and enzymes. Cell-free protein synthesis is a powerful flexible bottom-up approach that while utilizing minimum of cellular elements allows for labor- and time-efficient protein expression in a test tube without multistep complex maintenance of a living culture. Membrane proteins and cell machineries whose functions critically depend on interface with lipid bilayer environment, e.g. G-protein-coupled receptor, cytochrome P450 oxygenases and rhodopsins, have been expressed cell-free in soluble function-preserved form as supramolecular complexes using the nanodiscs artificial membrane detergent-free technology. The nanodiscs represent lipid bilayer nanoparticles (FIG. 4) with controllable dimensions which self-assemble with helical protein “belts” (membrane scaffold protein, assigned as 1E3D1). Dimensions and high degree of homogeneity of the nanodiscs are securely controlled by the length of the scaffold protein. Thus far, the cell-free nanodiscs approach has been mainly applied for structural biology (including NMR, EPR, X-ray and neutron scattering protein characterization), peptide- and protein-membrane interactions studies and single molecule measurements. Other applications include phage-display drug development, microfluidic on-demand point-of-care therapeutic protein expression and designer vaccine for cancer immunotherapy.